• Title/Summary/Keyword: ROTATIONAL FRICTION

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A Study on Tribological Properties of Magneto-Rheological Fluid (MRF) in Polishing Process (연마공정에서 MR 유체의 트라이볼로지적 성질에 대한 연구)

  • Lee S.O.;Jang K.I.;Min B.K.;Lee S.J.;Seok J.
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 2006.05a
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    • pp.497-498
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    • 2006
  • Tribological properties of a Magneto-Rheological(MR) fluid in a polishing process are studied. For this polishing process, abrasive wear model is proposed as a function of shear force, normal force and actual mean velocity of MR particles at workpiece surface. Experimental conditions are changed by varying the gap distance between workpiece and tool and the rotational speed of tool. From the experimental results, a modified Stribeck curve is obtained, and the friction coefficient turns out to have linear relationship with a modified Sommerfeld number. The validity of the wear model is supported by additional experiments performed for measuring material removal rates.

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Development of a Static Pressure Radial Air Bearing and Estimate of Design Variables (정압형 레디얼 공기베어링 개발 및 설계인자 영향 평가)

  • Kim, Ock-Hyun;Lee, Kyu-Ho
    • Journal of the Korean Society of Manufacturing Technology Engineers
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    • v.21 no.3
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    • pp.502-506
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    • 2012
  • Air bearing is characterized by its extremely low friction and cleanliness such that it is widely used especially for spindles with ultra-high rotational speed at several tens of thousands rpm. This paper contributes to design of a static radial air bearing suggesting numerical analysis to anticipate its performances. The numerical analysis is an iteration method based on finite difference formulation of the Reynolds equation. A prototype air bearing has been designed and manufactured. Its load capacity has been measured and compared with the numerical solutions. The result shows good consistency between the experiment and theory, which informs that the numerical analysis can be used as an useful tool to anticipate the performances. Effects of design variables on the bearing performance have been examined by Taguchi's experimental methods using orthogonal array. Number of holes for supplying pressurized air, clearance between shaft and bearing, the hole diameter and bearing length are chosen for the design variables. The result shows that the clearance and the bearing length are the most influential variables while the others can be considered as almost negligible.

The analysis of the resonance characteristics of a traveling wave type ultrasonic motor by applying the normal force and driving voltage (진행파 회전형 초음파 모터의 가압력과 구동전압에 따른 공진특성의 변화 분석)

  • Oh, Jin-Heon;Park, Cheol-Hyeon;Lim, Kee-Joe;Kim, Hyeon-Hoo
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2008.06a
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    • pp.324-324
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    • 2008
  • Piezoelectric ceramics is an active element that makes stator to vibrate to generate rotational force in ultrasonic motors. In drive of ultrasonic motors, many factors that affect to the resonance characteristics of piezoelectric ceramics exist. For example, those factors are bonding condition with elastic body, the magnitude of electric field, the normal force for frictional drive and the emission of heat due to vibration and friction and so on. Therefore, it is important to research the inclination of property variation of piezoelectric ceramics in circumstance that has complex elements. In this paper, we focused and analyzed the resonance characteristics of ultrasonic motor due to the magnitude of the driving voltage and normal force.

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Development of Compact Phase-difference Controller for an Ultrasonic Rotary Motor (회전형 초음파모터의 소형 위상차 제어기 개발)

  • Yi Dong-Chang;Lee Myoung-Hoon;Lee Eu-Hark;Lee Sun-Pyo
    • Journal of the Korean Society for Precision Engineering
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    • v.23 no.8 s.185
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    • pp.64-71
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    • 2006
  • In this paper, a uniform speed controller for an ultrasonic rotary motor is developed using the phase-difference method. The phase difference method uses traveling waves to drive the ultrasonic motor. The traveling waves are obtained by adding two standing waves that have a different phase to each other. A compact phase-difference driver system is designed and integrated by combining VCO(Voltage Controlled Oscillator) and phase shifter. Theoretically the relationship between the phase difference in time and the rotational speed of the ultrasonic motor is sine function, which is verified by experiments. Then a series of experiments under various loading conditions are conducted to characterize the motor's performance that is the relationship between the speed and torque. Proportional-integral control is adopted for the uniform speed control. The proportional control unit calculates the compensating phase-difference using the rotating speed which is measured by an encoder and fed back. Integral control is used to eliminate steady-state errors. Differential control for reducing overshoot is not used since the response of ultrasonic motor is prompt due to its low inertia and friction-driving characteristics. The developed controller demonstrates reasonable performance overcoming disturbing torque and the changes in material properties due to continuous usage.

Estimation of the Cutting Torque Without a Speed Sensor During CNC Turning

  • Kwon, Won-Tae;Hong, Ik-Jun
    • Journal of Mechanical Science and Technology
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    • v.19 no.12
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    • pp.2205-2212
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    • 2005
  • In this paper, the cutting torque of a CNC machine tool during machining is monitored through the internet. To estimate the cutting torque precisely, the spindle driving system is divided into two parts: electrical induction motor part and mechanical part. A magnetized current is calculated from the measured three-phase stator currents and used for the total torque estimation generated by a spindle motor. Slip angular velocity is calculated from the magnetized current directly, which gets rid of the necessity of a spindle speed sensor. Since the frictional torque changes according to the cutting torque and the spindle rotational speed, an experiment is adopted to obtain the frictional torque as a function of the cutting torque and the spindle rotation speed. Then the cutting torque can be calculated by solving a $2^{nd}$ order difference equation at a given cutting condition. A graphical programming method is used to implement the torque monitoring system developed in this study to the computer and at the same time monitor the torque of the spindle motor in real time through the internet. The cutting torque of the CNC lathe is estimated well within an about $3\%$ error range in average in various cutting conditions.

Behaviour of a plane joint under horizontal cyclic shear loading

  • Dang, Wengang;Fruhwirt, Thomas;Konietzky, Heinz
    • Geomechanics and Engineering
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    • v.13 no.5
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    • pp.809-823
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    • 2017
  • This paper describes lab test results of artificial rock-like material samples having a plane joint. Cyclic shear tests were performed under different normal loads and different shear displacement amplitudes. For this purpose, multi-stage normal loading tests (30 kN, 60 kN, 90 kN, 180 kN, 360 kN and 480 kN) with cyclic excitation at frequency of 1.0 Hz and different shear displacement amplitudes (0.5 mm, 1.0 mm, 2.0 mm, 4.0 mm, 5.0 mm, and 8.0 mm) were conducted using the big shear box device GS-1000. Experimental results show, that shear forces increase with the increase of normal forces and quasi-static friction coefficient is larger than dynamic one. With the increase of normal loads, approaching the peak value of shear forces needs larger shear displacements. During each cycle the normal displacements increase and decrease (rotational behavior in every cycle). Peak angle of inclination increases with the increase of normal load. A phase shift between maximum shear displacement and maximum shear force is observed. The corresponding time shift decreases with increasing normal load and increases with increasing shear displacement amplitudes.

Characteristics of tidal current and mean flow at the west channel of Yeoja Bay in the South Sea of Korea (여자만 서수도 해역의 조류 및 조석평균류 특성)

  • CHOO, Hyo-Sang
    • Journal of the Korean Society of Fisheries and Ocean Technology
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    • v.55 no.3
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    • pp.252-263
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    • 2019
  • In order to understand the tidal current and mean flow at the west channel of Yeoja Bay in the South Sea of Korea, numerical model experiments and vorticity analysis were carried out. The currents flow north at flood and south at ebb respectively and have the reversing form in the west channel. Topographical eddies are found in the surroundings of Dunbyong Island in the east of the channel. The flood currents flow from the waters near Naro Islands through the west channel and the coastal waters near Geumo Islands through the east channel. The ebb currents from the Yeoja Bay flow out along the west and the east channels separately. The south of Nang Island have weak flows because the island is located in the rear of main tidal stream. Currents are converged at ebb and diverged at flood in the northwest of Jeokgum Island. Tidal current ellipses show reversing form in the west channel but a kind of rotational form in the east channel. As the results of tide induced mean flows, cyclonic and anticyclonic topographical eddies at the northern tip but eddies with opposite spin at the southern tip are found in the west channel of Yeoja Bay. The topographical eddies around the islands and narrow channels are created from the vorticity formed at the land shore by the friction between tidal currents and the west channel.

Study on mechanical behaviors of loose mortise-tenon joint with neighbouring gap

  • He, Jun-xiao;Wang, Juan;Yang, Qing-shan;Han, Miao;Deng, Yang
    • Structural Engineering and Mechanics
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    • v.77 no.4
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    • pp.509-521
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    • 2021
  • The neighbouring gaps at the mortise-tenon joint in traditional timber structure, which leads to the complexity of the joint, are considered to impair the mechanical performance of the joint. In this paper, numerical simulation of loose joint was conducted to examine the deformation states, stress distributions, and bearing capacities, which was verified by full-scale test. On the basis of the experimental and numerical results, a simplified mechanics model with gaps has been proposed to present the bending capacity of the loose joint. Besides, the gap effects and parameter studies on the influences of tenon height, friction coefficient, elastic modulus and axial load were also investigated. As a result, the estimated relationship between moment and rotation angle of loose joint showed the agreement with the numerical results, demonstrating validity of the proposed model; The bending bearing capacity and rotational stiffness of loose joint had a certain drop with the increasing of gaps; and the tenon height may be the most important factor affecting the mechanical behaviors of the joint when it is subjected to repeated load; Research results can provide important references on the condition assessments of the existing mortise-tenon joint.

Tribological behavior of concrete with different mineral additions

  • Belaidi, Amina;Hacene, Mohammed Amine Boukli;Kadri, El-Hadj;Taleb, Omar
    • Advances in concrete construction
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    • v.11 no.3
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    • pp.231-238
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    • 2021
  • The present work aims at investigating the effects of using various fine mineral additions as partial replacement to Portland cement on the tribological properties of concrete. To achieve this goal, concrete mixtures were prepared with different percentages (10, 20 and 30%) of limestone fillers (LF) and natural pozzolana (NP), and (20, 40 and 60%) of blast furnace slag (BFS). The interface yield stress (τ0) and viscous constants (η) that allow characterizing friction at the concrete-pipe wall interface were determined using a rotational tribometer. In addition, the compositions of the boundary layers that formed in the pumping pipes of the different concretes under study were also identified and analyzed. The experimental results obtained showed that the concretes studied have a linear tribological behavior that can be described by the Bingham model. Furthermore, the use of different mineral additions, especially limestone fillers and blast furnace slags, even at high rates, had a beneficial effect on the optimization of the volume of paste present in the boundary layer, which made it possible to significantly reduce the viscous constant of concrete. However, a maximum rate of 10% of natural pozzolana was recommended to achieve tribological properties that are favorable to the pumpability of concrete.

A Dynamic Modeling & State Sensitivity Analysis of the Surface Mounting Device (Surface Mounting Device의 동역학적 모델링 및 상태 민감도 해석)

  • Jang, Jinhee;Han, Changsoo;Kim, Jungduck
    • Journal of the Korean Society for Precision Engineering
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    • v.13 no.7
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    • pp.90-99
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    • 1996
  • In the area of assembly process of micro-chips and electronic parts on the printed circuit board, surface mounting device(SMD) is used as a fundamental tool. Generally speaking, the motion of the SMD is based on the ball screw system operated by any type of actuators. The ball screw system is a mechanical transformed which converts the mechanical rotational motion to the translational one. Also, this system could be considered as an efficient motion device against mechanical backlash and friction. Therefore a dynamic modeling and state sensitivity analysis of the ball screw system in SMD have to be done in the initial design stage. In this paper, a simple mathematical dynamic model for this system and the sensit- ivity analysis are mentioned. Especially, the bond graph approach is used for graphical modeling of the dynamic system before analysis stage. And the direct differentiation method is used for the state sensit- ivity analysis of the system. Finally, some trends for the state variables with respect to the design variables could be suggested for the better design and faster operating based on the results of dynamic and state sensitivity.

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